1. Field of the Invention
The invention relates to a polyaxial bone anchoring device with an enlarged pivot angle. The polyaxial bone anchoring device includes a bone anchoring element for anchoring in a bone and a receiving part for coupling a stabilization rod to the bone anchoring element. The receiving part includes a rod receiving portion for receiving the rod and a head receiving portion that is flexible so as to allow introduction and clamping of a head of the bone anchoring element. A locking ring is provided for compressing the head receiving portion of the receiving part to lock the head. A bounding edge of the head receiving portion is configured to permit the anchoring element to pivot at a larger pivot angle relative to the receiving part at a first location of the bounding edge than at a second location of the bounding edge. The head receiving portion is rotatable with respect to the rod receiving portion, so that an orientation or direction of the larger pivot angle can be selected.
2. Description of Related Art
A polyaxial bone anchoring device with an enlarged pivot angle is described in U.S. Pat. No. 6,736,820. This bone anchoring device includes a bone screw and a receiving part with a seat for the head of the bone screw. The screw member can be pivoted to at least one side by an enlarged angle, because the edge of the free end of the receiving part is of asymmetric construction.
Another polyaxial bone anchor is described in US 2005/0080415 A1. This bone anchor has a body member having a U-shaped channel for receiving the rod and a compressible recess for receiving a head of the anchor member such that the anchor member can initially polyaxially angulate with respect to the body member and further has a collar slidably disposed about the body member and capable of compressing the recess around the head. The lower bounding edge of the body member may include a countersunk region to permit increased angulation when the anchor member is oriented toward the countersunk region.
US 2007/0118123 A1 describes a polyaxial bone anchor with increased angulation. The polyaxial bone anchor has a locking element shaped and configured to allow an anchoring member, e.g. a screw or a hook, to polyaxially rotate at large angles about a central axis of the bone anchor before compression locking the anchoring member within an anchor head.